"I don't think if anything prevents your from using your Mac during the print. You just have to be careful not to use expośe gesture and Mac dashboard during print."

Which is to say that it's very hard to use a Mac at the same time as you're printing in case your mouse curser goes to the 2nd screen, something takes over the second screen with another space, etc. And this is if you're OK with turning off per-screen spaces and menus, which seriously gets in the way of my other work.

Oh, and you'd better make sure you never use a screen-saver (BAD for expensive IPS monitors), and that the desktop background on your projector "screen" is pure black. Because sometimes the printer will glitch and project the desktop background on the print bed, and you won't know it until your print fails.

In the end I opted for a Mac Mini as my dedicated machine for both my 3D printers. Instead of buying a monitor for it, I used an HDMI dummy plug to fool it into thinking it has a monitor. Then I hooked it up to my main mac via a Thunderbolt cable. Then I use screen sharing to bring it up as a space on my main mac when I need to see it.

A bonus to this is that I can tell the screen-sharing app to show me any or all of the Mini's "screens" at once. So that I can see exactly what is being fed to the projector.

Yeah, I'm using my sole iMac right now and it's a bit of a pain as I'm too paranoid to use it while printing. I'm currently in the market for a Mac Mini to serve as a dedicated print 'server'. Good call on the Thunderbolt cable spoof for it's video.